Ink jet printers form an image on a substrate by ejecting drops of ink from a cartridge assembly toward a substrate, which is typically a paper media. The ink drop is ejected through a nozzle by an ink energizer on a semiconductor chip. The energizer may be a device such as a heater or a piezoelectric device. The ink energizer works by receiving an electrical current and transforming the energy in the electrical current into a pressure pulse or heat, some of which is transferred into the ink causing the ink to be ejected through the nozzle toward the print media. Much of the energy from the electrical current provided to the chip ends up as heat.
Not all of the heat produced by the energizer is transferred into the portion of the ink that is immediately ejected from the nozzle. Some of the ink which receives the heat remains in the area of the printhead adjacent the chip or in the ink reservoir. The heat in the components also tends to be transferred to the ink remaining in the printhead or in the ink reservoir. If the ink remaining in the printhead receives the excess heat at a sufficiently small rate, then the ink is able to dissipate the heat through other components of the printhead or ink reservoir. However, if the ink remaining in the printhead or reservoir receives heat at a rate above that at which the heat can be dissipated, then the temperature of the ink may rise excessively. This increase in ink temperature can cause problems with the functioning of the cartridge.
For example, as the temperature of the ink increases, dissolved gases in the ink will tend to separate from the ink, and form gas bubbles. The bubbles act as obstructions in the flow channels of the cartridge, blocking the flow of ink to the nozzles and reducing print quality. In addition, the change in ink temperature, further compounded by the separation of dissolved gases from the ink, tends to change the viscosity of the ink. This affects the mass and velocity of the ink drops that are ejected from the nozzles, and again, reduces print quality. Thus, for these and other reasons, controlling heat transfer within the printhead tends to be a very important consideration in ink jet printhead design.
Other printhead design considerations tend to exacerbate the problem of ink heating, rather than alleviate it. For example, consumers prefer printers that operate faster. One common method of achieving this design goal is to fire the energizers at a faster rate and produces smaller ink droplets. A faster firing rate puts heat into the ink at a faster rate. Thus, the printhead components tend to heat up and warm the ink remaining in the printhead.
Furthermore, printers having a higher print resolution are more preferred. One method of achieving this design goal is to place the energizers closer together, so that more ink droplets can be formed within in a given surface area. Each of the ink droplets may also be smaller. Not only does an increase in energizers increase the printhead and ink temperatures, but smaller ink droplets tend to transfer heat away from the printhead with much less efficiency than the heat transferred by larger ink droplets. Thus, some preferred design goals tend to increase the problem of ink and printhead component heating.
Some ink jet printheads have been designed to dissipate heat in a more efficient manner. However, these cartridges typically require complicated assembly methods and customized parts which tend to increase printers costs significantly. Further, these complex printheads tend to use components which are not sufficiently resistant to ink induced corrosion. Accordingly as the components are exposed to the ink, corrosion of the components may cause the components to fail or the ink to be contaminated.
An object of the invention is to provide an improved printhead assembly for an ink jet printer.
Another object of the invention is to provide a printhead assembly which is cost effective to make.
Still another object of the invention is to provide a printhead of improved design which more effectively removes excessive heat from the printhead assembly.
Another object of the invention is to provide a printhead assembly which reduces the exposure of various components to corrosive materials.
Yet another object of the invention is to provide a printhead structure suitable for use with higher energy higher speed printhead.